1. Field of the Invention
This invention relates generally to semiconductor diodes. More particularly, the present invention relates to a surface mounting type diode which has a very small size of about 1 mm for each of length, width and height.
2. Description of the Prior Art
There has been an increasing requirement for size reduction with respect to diodes, like other semiconductor devices, thereby enabling high-density mounting of electronic components on circuit boards. At present, diodes with a size of about 1 mm for each of length, width and height are available. Further, it is convenient to use diodes of the surface mounting type for facilitating mounting to the circuit board.
FIG. 6 of the accompanying drawings shows a typical prior art diode of the surface mounting type. Specifically, the prior art diode designated by reference numeral 11 comprises a molded resin package 12 having a flat bottom surface 12a. The resin package 12 is square or rectangular in plan view and has a very small size of about 1 mm for each of the length, width and height.
The diode 11 further comprises a pair of leads 13, and a semiconductor diode chip 14 bonded on one of the leads 13 in electrical connection therewith. The chip 14 is electrically connected to the other lead through a metal wire 15.
Each of the leads 13 has a first bend 13a closer to a higher inner end 13c, and a second bend 13b closer to a lower outer end 13d. Between the first and second bends 13a, 13b is a vertical intermediate portion 13e. The outer end 13d has a flat mounting surface 13f which is used for mounting the diode 11 onto a printed circuit board (not shown).
In manufacture of the prior art diode 11, use is made of a mold which includes an upper mold member 17 having an upper molding cavity 17a, and a lower mold member 18 having a lower molding cavity 18a, as indicated by phantom lines in FIG. 6. The paired leads 3, which may be initially connected to a leadframe (not shown), need be held straight between the respective mold members 17, 18 at the time of molding the resin package 12. After molding the resin package 12, the mold is opened, and the respective leads 3 are cut off from the unillustrated leadframe. Then, each of the leads 3 is bent at two positions 13a, 13b in a manner such that the flat mounting surface 13f of the lead outer end 13d is generally flush with the flat bottom surface 12a of the resin package 12.
According to the prior art arrangement, the inner end 13c of each lead 13 is enclosed in the resin package 12, whereas the respective bends 13a, 13b are located outside the resin package 12. Such an arrangement has been found to give rise to the following problems.
First, since the respective bends 13a, 13b of each lead 13 are positioned outside the resin package 12, it is necessary to perform bending of the lead 3 after forming the resin package 12. Thus, it is extremely difficult or virtually impossible to make the flat mounting surface 13f of the lead outer end 13d accurately flush with the flat bottom surface 12a of the resin package 12.
As a result, the flat bottom surface 12a of the resin package 12 may not be utilized for stably supporting the diode 11 on the printed circuit board, and the support must be provided only by the mounting surface 13f of the lead outer end 13d which is much smaller in area than the bottom surface 12a of the resin package 12. Due to the instability of support, the diode 11 may be improperly mounted on the circuit board. This problem will be particularly remarkable when mounting of the diode 11 is performed by a high-speed mounter which inevitably causes vibration.
Secondly, due to the necessity of bending each of the leads 13 after the formation of the resin package 12, the projecting portion of the lead must be rendered relatively long for facilitating subsequent bending of the lead. Therefore, the length or height of the vertical intermediate portion 13e of the lead becomes inevitably large after bending, and the gravitational center of the diode 11 is also located at a relatively high position, further adding to the instability of support. Further, the long projecting portion of the lead also results in difficulty of reducing the overall size of the diode.